1. Field of the Invention
The present invention relates to an apparatus for detecting radiation and a method for manufacturing such apparatus. More particularly, the invention relates to an apparatus for detecting radiation using a semiconductor, such as amorphous silicon representing non-crystalline semiconductor, and relates to a method for manufacturing such an apparatus.
2. Related Background Art
There have been proposed various methods for detecting radiation by combining a photodetector and phosphor in various ways. Also, it is possible to obtain positional information or image information by dividing a photodetector into a plurality of pixels. In this case, if phosphor is arranged all over the pixels uniformly, not only does fluorescence enter a photodetector immediately beneath the phosphor, but also, unwanted fluorescence enters the photodetectors adjacent to the phosphor. This decreases the resolution of images.
In order to prevent decreased resolution; there have been proposed, for example, a preventive means as disclosed in Japanese Patent Laid-Open Application No. 53-96789 wherein partition plates are provided between photodetectors to prevent light from breaking through a particular photodetector, and phosphor is buried in each portion thus partitioned, and also, as disclosed in Japanese Patent Laid-Open Application No. 5-60871 wherein a substrate having a plurality of recessed portions is arranged, and phosphor is buried in each recessed portion to make it a radiation detector by adhesively bonding such substrate to a photodetecting panel having a plurality of pixels.
FIGS. 1 to 3 illustrate these examples. Now, for example, a structure is arranged as shown in FIG. 1 so that a fluorescent plate 6 is provided on the radiation incident side, and the incident radiation is transformed into visible light in the fluorescent plate 6, thus being converted into electric signals when it is incident upon a semiconductor photodetection element 2.
Also, as shown in FIG. 2, a structure is arranged so that a fluorescent plate 6 is divided and provided separately for each of the pixels on a semiconductor photodetector 2, and the incident radiation is transformed into visible light in the fluorescent plate 6 thus separated for each pixel, and that such light is converted into electric signals when it is incident upon each of the pixels of the semiconductor photodetection element 2.
Or, it is possible to cite a structure arranged as shown in FIG. 3. The structure is such that a fluorescent plate 6, which is divided into each of the pixels, is arranged on the side opposite to the incident side of radiation, and the incident radiation is directly converted into electric signals per pixel by means of the semiconductor fluorescent detection element 2. Further, the radiation having passed the semiconductor photodetection element 2 is transformed into visible light by means of the fluorescent plate 6 which is divided per pixel. The visible light is converted into electric signals when it is incident upon each of the pixels of the semiconductor photodetection element 2.
However, the method in which phosphor is buried in each portion separated by partition plates has a problem that any defects that may be found after the completion of the phosphor coating process, such as sensitivity unevenness and point defective of phosphor, tend to make the expensive photodetecting portion eventually defective.
Also, the method in which phosphor is buried in a substrate provided with a plurality of recessed portions for the formation of a radiation detector, which is adhesively bonded to a photodetecting panel having a plurality of pixels, often presents a problem that the substrate becomes weaker due to many numbers of recessed portions. As a result, damages is caused or its handling is made difficult in some cases. Also, it is necessary to make the aperture ratio greater particularly when improving its efficiency. In other words, the ratio of the size of recessed portion should be made larger. Such problems, as described above, are serious.
These radiation detectors also present a problem that the interface between phosphor and the recessed portions or partition plates is partially peeled off due to bending stress at the time of handling, hence causing the reflectance of light to vary at the recessed portions or partition plates per pixel. This generates image unevenness in some cases.
For the structures described above in conjunction with FIGS. 1 to 3, there are also aspects yet to be improved as given below.
In accordance with the structure shown in FIG. 1 that uses the phosphor having no pixel separation, when the incident radiation, which is transformed into visible light in the phosphor, is allowed to be incident upon adjacent pixels of a semiconductor element, so-called cross-talks between pixels results, thus making it impossible to obtain the exact image of a target image in some cases.
In accordance with the structure shown in FIG. 2, that uses the phosphor having separated pixels, it is possible to eliminate the cross talks referred to in the preceding paragraph, but there is no specific means for separation when making the pixel pitches finer to increase the resolution, and also, when making the thickness of phosphor larger in order to enhance the sensitivity. As a result, there is a limit to obtaining a higher resolution and sensitivity in some cases.
In accordance with the structure shown in FIG. 3, it is possible to anticipate some effect when a semiconductor photodetecting element formed by mono-crystalline semiconductor, but it is impossible to convert radiation into electric signals directly by means of an apparatus using amorphous semiconductor, such as a --Si semiconductor, formed on an insulated substrate as an apparatus for detecting radiation, which should be capable of dealing with an image having a large area. Therefore, it is still impossible to solve those problems as described above depending on the situation.